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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        //1,1,2,3,5,8,13,21,34,55,89
        function fn(n) {
            if (n === 1 || n === 2) {
                return 1
            }
            return fn(n - 1) + fn(n - 2)
        }
        console.log(fn(5));
        //4,3,3,2,
    </script>
</body>

</html>